Vibration motors are commonly used in mobile communication devices to quietly notify a user of incoming calls without disturbing other people. A typical vibration motor uses an eccentric rotor to convert electromagnetic energy into vibration energy to generate an alert. A coil (electromagnet) produces an alternating magnetic field which interacts with the rotor and causes the rotor to rotate. Both cylindrical and planar vibration motors have been proposed and fabricated. In mobile communication devices, a planar vibration motor is more desirable because it can be made thinner. In a typical planar vibration motor, the eccentric rotor assembly in placed inside the motor. A shaft is needed to support the rotor assembly during rotation and to transfer the vibration energy to the housing of the motor, and ultimately to the user. The mechanical contact and friction between the shaft and a supporting bearing often pose reliability problems because of tear and wear. Some of the energy is wasted in the form of heat generated from the friction. Also, besides the shaft and bearing, a few more mechanical components such as an eccentric mass, brackets, etc., are needed for the operation of the device. These components make the structure more complicated and increase the manufacturing cost.
Therefore, it would be highly desirable to provide a simple, planar, highly reliable, and low power vibration motor for mobile communication devices as well as other applications.
It is a purpose of the present invention to provide a new and improved vibration motor which possesses the above desirable features.